Use of the conventional anti-heat, anti-wear materials in the internal combustion engine becomes increasingly difficult as the engine becomes smaller and accordingly its load becomes higher.
Especially for valve seat, valve lifter and various seals in the engine using lead-free gasoline, development of materials superior in anti-heat, anti-wear properties is urgently demanded.
Strong materials presently available include sintered alloys of iron and copper, iron and phosphorus, and iron and boron, which are, however, inferior in anti-heat, anti-wear properties and these are found unfit for parts requiring high anti-heat and anti-wear.
High phosphorus cast iron is well-known as an anti-wear material, but being liable to cause blowholes or poor flow of molten metal, the phosphorus content has to be limited to a range of 0.3-0.6%.
Further, there is an improved high phosphorus cast iron, which represents a phosphorus cast iron added with boron, but even this one fails to meet the strength requirements presently demanded of anti-heat, anti-wear materials, because the additions of phosphorus and boron are restricted for technical reasons of casting. Moreover, a cast iron with contents of phosphorus and boron, which develops flaky precipitation of graphite, lacks mechanical strength and is found unfit for service where high strength is required.